


Restless

by yay_for_absurdism



Series: Just a Scientific Favor [3]
Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: First Time, Fluff and Smut, M/M, Senku finally realizes his feelings for Gen, Senku made Gen's deck of cards and I refuse to entertain any other possibility, homoerotic sex scene
Language: English
Status: Completed
Published: 2020-04-28
Updated: 2020-04-28
Packaged: 2021-03-02 02:48:11
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 8,248
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23897755
Author URL: https://archiveofourown.org/users/yay_for_absurdism/pseuds/yay_for_absurdism
Summary: Senku finally realizes that he’s in love with Gen, and comes up with a plan on how to tell the mentalist how he feels.
Relationships: Asagiri Gen/Ishigami Senkuu
Series: Just a Scientific Favor [3]
Series URL: https://archiveofourown.org/series/1643647
Comments: 9
Kudos: 321





	Restless

**Author's Note:**

> Yeehaw, the third and final part of this series! 
> 
> There are a couple references to the prior two works in this series, so it might help to read those but it's not absolutely necessary. 
> 
> Enjoy!

Probably far too late, Senku realized something. 

No, not too late as in _oh no, the fact that it took me so long to realize this is a disastrous flaw and it means that everything is going to fall apart_. It was more like _oh no, how on earth could it have taken me so long to realize this, how can I call myself a scientist if I’m this oblivious to pertinent information_. 

In his defense, though, the matters of the mind and thought and emotions and psychology and those sorts of “soft” sciences were not his domain of expertise. And that was what his little discovery was about. 

He sighed, putting his head in his hands. 

How inconvenient. 

He’d fallen in love. 

He had never expected to fall in love. At this point, from only ever feeling interested in people due to their scientific usefulness, he had assumed he would never ever, not in a billion years, fall in love. He’d never been interested in anyone in that way, he hadn’t even payed it any mind. And, like any sane person would, he’d found Taiju and Yuzuriha’s overwhelmingly obvious love for each other disgusting and distracting. Love was, simply, a distraction. And a soft science. Sure, there was the whole thing about pheromones and chemicals in the brain and yes there was some real science to love. But there was also the irrational part, the psychology of it all. And that wasn't his forte, no, that was more Gen’s forte. 

Like it often did, his mind circled back to Gen. 

He had assumed that it was just because Gen was an insufferable nuisance who managed to worm his way into everyone’s thoughts. He was a showman, a mentalist, that was his shtick. And he was good at what he did, so of course people couldn’t help but think about him. And Senku was a person too, so it made logical sense that even if he was rather resistant to Gen’s tricks, he would still get pulled into the mentalist’s mind games a little bit. 

But hindsight was 20/20, and now looking back at his own thoughts and actions pertaining to Gen, he could see that his reactions were not just the normal expected reactions to psychological tampering and conditioning. They were something more. 

Senku rubbed his eyes, looking at the plans sitting on his workbench that he’d been working on. Plans he hadn’t touched in over a half hour. Somehow, even though Gen wasn’t even physically present, the mentalist was still distracting him. 

Well, his mind was too busy with _other_ topics to work right now. He folded the plans up, organized the bench and put away his beakers and chemicals, and climbed up to his observatory. It was still far too early to use the telescope, the sun was still a few degrees above the horizon and the stars would not be visible for quite a while. But the sky was almost cloudless and bathed in a cacophony of red and orange and pink hues, a sunset that was unique to the stone world without any high-rises and pollution to obscure and dampen the colors. So he leaned against the railing, watching the sun dip lower and lower and the colors grow darker and more saturated until the sky was metaphorically on fire. 

So. Gen. He was in love with Gen, a fact he had come to terms with just recently. 

Alright, just think about this logically. That was the best thing to do in a situation he had no practical experience with. 

He had a few options here. One, tell Gen about his feelings. Two, say nothing and live with all these feelings inside of him. Three, say nothing and not have these feelings anymore, either by waiting until they go away or forcing them away. But, then, which one was the best, most logical option to choose? 

He could ask someone what to do. Someone with more experience. Someone he trusted who was smart and logical and relatively mature and knew about emotions and relationships and all that. But who? Oh, right, there wasn’t a single person in the Kingdom of Science who fit all of those criteria except Gen. 

Fuck. 

Senku sighed, running a hand through his hair. Maybe it would be best to say and do nothing. He could live with suppressing his feelings, right? 

Love and relationships were a distraction anyway. The last thing he, and the Kingdom of Science, needed was for him to be distracted. He was the only one with the sum of all human scientific advancements stored away in his brain; he needed to be one billion percent focused on the tasks at hand. 

A noise from the entrance of the observatory startled him out of his thoughts, and he turned to see Gen climbing up to join him. 

“Looks like the clouds cleared up and we’ll have a clear night.” the mentalist said, walking over and joining Senku at the railing. 

“A perfect night for a bit of mapping.” 

“I would have thought that you would have finished mapping the stars by now.” Gen said, resting his chin on the back of his hand. His ivory hair shone in the very last bit of sunlight that still clung to the horizon. 

“The stars change every season. It’ll take a year to finish.” 

“Ah. Of course.” 

Soon, it was dark enough that the moon was high and bright and the stars were twinkling amid the clear black sky. Senku went to turn away from the railing and set up the telescope, but he stopped dead, eyes fixed on Gen. It didn’t make sense, he saw Gen every day, he even saw Gen in the moonlight on a regular basis. There was no reason that the sight of the mentalist looking up at the stars, expression soft and eyes half lidded and lips shaped into a tiny smile, should make Senku’s heartbeat quicken and cheeks heat up and thoughts derail. It was one billion percent illogical. 

And then Gen turned to look at him, fixing him with those blue-grey eyes that shone like the stars, and he felt his heart figuratively leap in his chest. 

He had to say something about his feelings. He was one billion percent sure of that. Now, he only had to figure out how. 

.....

Senku paused, on his way from his and Chrome’s shared hut to the village, to watch Gen for a moment. The mentalist had been roped into helping Kaseki, and was listening with a look of dismay as the old man explained the next task at hand. He chuckled. He was one billion percent sure he’d hear all about the “grueling” task tonight when Gen came to him to complain. 

He noted, though, that Gen was playing with the hem of his sleeves as he listened, picking at a loose thread with his forefinger and thumb. 

Ah, yes, the mentalist had a habit of keeping his hands busy. Not with work, of course, it just seemed that he liked to have something to keep his restless fingers moving. A fact that often went unnoticed because he usually kept his hands hidden within his long sleeves, but Senku had watched him enough to notice these sorts of minute details. 

Being a hack stage magician was quite the apt career path for someone with restless hands. 

At that moment an idea came to Senku, and if anyone had been watching him they would have seen his face twist into one of his signature sinister grins. 

Now he was excited. 

.....

He was going to make Gen a deck of cards. All magicians needed a deck of cards, and this stone world had thus far not provided Gen with such an accessory. Luckily, Senku was this world’s provider of extinct modern technology. And perhaps a deck of cards was very low on the totem pole of technology that needed to be revived, but Senku figured that he could be a little bit selfish, just this once. Hey, depending on how you rationalized it, this was an important invention for the Kingdom of science. 

At a minimum, it would at least give Gen more ways to trick people. 

As Senku saw it, he wasn’t the best with words, especially when it came to speaking about matters of the heart. Ugh, how corny. How gross. But anyways. He had no idea how to confess to someone in any way except just walking up and saying, point blank, “I like you”. Now it sort of made sense why it had taken Taiju five years to figure out how he wanted to confess to Yuzuriha. 

But once upon a time he’d bought Gen’s loyalty with cola. Maybe he could get his feelings across with another gift. 

Gen was a materialistic man, to his own admission, someone who was selfish and coveted the finer things in life. So it made sense to confess with a materiel object. Yes, that definitely seemed logical. 

Senku sat down at his workbench with Chrome snoring softly behind him. Time to get to work 

Paper was easy. They had plenty. Waterproof lacquer was easy, the village had had that before he’d arrived. Ink was relatively easy, he managed to make a few colors that should hold up well over time. Coming up with concepts for the cards was easy enough, he only had to think of fifty-two scientific concepts and theories. Well, fifty-three including the jokers (which would be the same). 

He wanted the cards to be a reflection of the Kingdom of Science. Or, more specifically, a coming-together of Gen’s “magic” and Senku’s science. Or, most specifically, Senku wanted the cards to remind Gen of him. 

Which was entirely extraneous, and frankly highly illogical, but hey. Love was illogical. Senku figured that was reason enough to be a bit emotional with his crafting of the cards. 

The hardest part, though, was drawing on the cards. He had a steady hand and could write as neatly and consistently as a typefont, but drawing was another matter. He could make simple diagrams well enough, he had a lot of experience with drawing up schematics, but the whole “artistic” aspect was lost on him. He was too logical for art, and had never excelled at drawing anything other than experiment blueprints. 

Eventually, he decided to keep the designs as simple as he could while still making the scientific concepts recognizable. 

With steady hands, he drew a tiny scar across the cheek of tiny joker-Gen. That scar that had somehow formed in a perfect representation of the mentalist’s personality. Not for the first time, Senku longed to run his finger along that scar, along the tiny groove that was proof of the 3700-year petrification they had shared. 

Senku smiled to himself, filling in the tiny joker-Gen's hat. If all went according to plan, and if his assumptions about Gen were correct, then maybe, soon, he would be able to. 

It took him twenty-seven days of working in his free time to complete the deck. So be it if it took longer than he had thought it would, he wanted the cards to be perfect. And looking at them, stacked neatly on his workbench, he could definitively, one billion percent, say they were. 

.....

Humans were, thankfully, creatures of habit, so there was a one billion percent chance that Gen would come climbing into the observatory about a half hour after the sun had set on a cloudless sky. And like clockwork, Senku heard the sound of bare feet climbing up the ladder exactly 1620 seconds after the sun had dipped below the horizon. 

“Good evening, Senku-chan.” the mentalist chirped, smiling his normal cheeky smile. 

“Hey Gen.” Senku replied, swallowing hard before giving Gen a hopefully completely normal-looking smile. He shouldn’t be nervous, but he was. 

If Gen noticed anything weird he didn’t mention it, and just came to sit in his normal spot a couple feet away from Senku and the telescope. Out of the corner of his eyes, Seknu watched him shift into a comfortable position, legs crossed and overcoat draped over his legs and feet to keep from getting cold. For not the first time, Senku thought about making Gen some shoes and forcing him to wear them because it was entirely illogical to be running around the stone world in bare feet. 

Slipping his hand into his side bag, Senku’s fingers closed around the deck of cards. He took a deep breath, and then another, forcing his parasympathetic nervous system to take back control of his body. 

“Gen.” he sat down, cross-legged, beside the mentalist. “Here.” 

He’d wrapped the deck in a small piece of leather, and tied it together with a length of rope he’d dyed a pinkish-red. An attempt to make it look pretty, but esthetics weren’t exactly his forte. 

Nevertheless, Gen beamed at him. “Oh, you made me another present?” his face lit up like a child’s on Christmas morning as he accepted the little package. Cute. “But I don’t remember asking for or needing anything.” 

Senku shrugged. “It’s not a necessity. But... I thought it might be something you’d like.” 

“Something I’d like? Ooh, how interesting. Let’s see what it is, then.” 

The mentalist pulled the string undone and hastily unwrapped his gift, but he stopped dead as he laid eyes on the stack of cards sitting in his hands. For a long moment he just stared, shocked, and then ran a finger over the lacquered back of the top card on the deck. 

“Oh, Senku.” Gen breathed, voice as soft and reverent as Senku had ever heard. “They’re beautiful.” 

Senku watched Gen expertly thumb through the deck, taking in each painstakingly hand-painted card with a look of absolute awe lighting up his face. Forget about the cards being beautiful (objectively they were just fine, Senku was no artist), Gen was the beautiful one here. 

Senku worked his bottom lip between his teeth, feeling a strange mix of panic, worry and excitement pool in the pit of his stomach. 

The mentalist chuckled, flipping one of the joker cards in his fingers and gazing at the little two-dimensional rendition of himself. “Aren’t I just the cutest?” he smiled, turning to look at Senku. 

The scientist had to bit his lip, hard, to stop himself from replying _yes, you are_. Instead, he asked. “Do you like them?” 

“I love them.” he thumbed through the cards once more, quickly, and then, once he’d gotten a good feel of the weight and size of the cards, began to shuffle the deck. It was an incredibly fluid action, his nimble fingers manipulating the cards with practiced ease. As to be expected from a stage magician. Either way, it was an impressive feat, a feat that no one else alive in the stone world would be able to perform. 

Senku could imagine Gen showing off his little card tricks to the villagers, and the look of absolute amazement on everyone’s faces in return. He smiled. 

“Pick a card, Senku-chan. Any card.” 

He looked at the cards fanned out in front of him. “I’m not going to participate in a card trick.” 

Gen pouted. “Indulge me.” 

Of course, he did. He picked the card Gen wanted him to pick. 

“You know what I’m doing, don't you?” 

“Of course. One billion percent.” 

Gen snatched the card from him, and placing it back in the deck, began to absentmindedly reshuffle. “You’re no fun.” he lamented, but looked anything but disappointed. His eyes were shining with happiness in the light of the moon. 

Alright. The plan had gone well so far. Now, for the next step, which was to- 

“Actually,” Gen said, interrupting Senku’s thought. His hands fell still. “I have a present for you too.” 

“Oh?” he hadn’t expected that. He watched Gen slip the deck of cards into one of his many pockets. 

“But you have to close your eyes for a minute while I get it. Ok?” 

From the smile on Gen’s face Senku could guess with a high degree of certainty that this was some sort of trick, but as he often did, he found himself indulging the mentalist. He closed his eyes, crossing his arms over his chest. “Just don’t take too long.” 

“I won’t.” 

In the darkness, he counted, and listened. He could hear Gen shuffling around, the sound of his multiple layers of clothing rustling as he moved. Sixteen, seventeen, eighteen... how long would he have to keep his eyes closed? Twenty-four, twenty-five... he could swear he could feel Gen close by, and if he really listened closely he could hear the mentalist breathing. Thirty-one, thrity-two... 

He felt his entire body twitch in surprise when Gen’s hands came to rest on his shoulders, and he felt his heart stop when Gen’s lips gently pressed up against his own. 

He couldn’t help it, his eyes shot open in surprise. His field of vision was filled with the black and white dichotomy of Gen’s hair, and then the beautiful blue-grey of Gen’s eyes as the mentalist pulled back from the short, chaste kiss. In his peripheral, he could see the corners of Gen’s mouth turned up in a smile. 

“I didn’t say you could open your eyes yet.” Gen said, shyly, averting his gaze as he pulled back. But he didn’t pull back very far, retreating only approximately twenty centimeters. And he didn’t take his hands off of Senku’s shoulders. 

Never had Senku’s mind been filled with so much chaos and clarity at the same time. On one hand, his brain was running a mile a minute analyzing the current situation. Gen had kissed him. Gen’s lips were so soft. His heartbeat was nearing 115 beats per minute, much higher than his average resting heartrate of 77. Gen had kissed him. That had been his first kiss. Gen looking shy was perhaps the best thing he’d laid eyes on in this stone world. Gen had kissed him. He could feel that his palms were sweaty, for some reason. _Gen had kissed him._

But on the other hand, one singular thought ran through his mind, much louder than the others. _I may not know much about love, but it would be illogical for Gen to kiss me if he didn’t have some sort of romantic feelings for me_. And despite everything, Gen was still a logical person. 

So Senku acted in the most logical way he could think of, given the circumstances. He reached out, pulling Gen close, and kissed him again. 

Each hand closing around a fistful of Gen’s coat, Senku pulled their bodies flush up against each other. Gen was effectively yanked into his lap, and with a yelp the two of them tumbled backwards, Senku landing on his back on the observatory floor with Gen sprawled on top of him. But after a moment of fumbling and Gen laughing, their lips met in another kiss, this time slow and long and sweet. Senku snaked his arms around Gen’s body, holding him close, and he felt the hands on his shoulders tighten, gripping the fabric of his tunic tightly. 

“You have no idea how long I’ve wanted to do that.” Gen breathed, as they pulled back just far enough to catch their breath. 

“Probably about as long as I’ve wanted to.” Senku replied. It wasn’t until he spoke that he found that he was out of breath. 

“Then, were all these favors you’ve done and presents you’ve made your way of trying to tell me how you feel?” 

“Uh. No.” Not consciously, at least. “Except the cards.” 

Gen smiled, giving Senku a short, soft kiss. “Well, I figured the cards were. I guess I’m more perceptive than you are.” 

“What?” What had he missed? 

“You dummy.” Gen kissed along his jawline. “The observatory.” 

The observatory had been a birthday present from the entire village. But it had been Gen’s idea. And Gen had taken the time to figure out his birthday. And then there had been Gen’s little speech... “You could have been more direct.” 

“How?” Gen sounded almost insulted as he kissed Senku’s cheek. “It was so romantic. And I literally, to your face, said I liked you.” 

“Like has a lot of connotations.” And obviously, he had picked up on the wrong connotation. 

The mentalist shook his head, chuckling softly as he kissed Senku’s forehead, over the tiny crevasse of one of his petrification scars. “You’re an idiot.” 

Objectively, he wasn’t. He was almost as far from an idiot as humanly possible. But he didn’t correct Gen, because he was pulled back into a deep kiss and Gen’s tongue found its way into his mouth and maybe now he sort of understood why so many people seemed to like kissing so much. Sure, he knew that kissing had positive effects on the body like releasing hormones such as oxytocin and dopamine and serotonin and lowering cortisol levels and decreasing blood pressure in a roundabout way. But in practice... kissing felt far better than what it promised in theory. 

Gen shifted on top of him, and the change of position drew a soft moan from his lips. Oh. Right. That was another effect that kissing could have on the body (when working together with other factors). 

“My my, Senku-chan.” Gen chuckled into the kiss. “Are you perhaps a little excited?” 

“Yes.” No use in lying. 

“Lucky me. I was worried you could only get excited for your beloved science.” 

He knew what Gen meant. He could hear a little bit of worry and relief in the mentalist’s voice, attempting to hide behind a joking tone. 

Senku shifted into a sitting position, with Gen sitting on his lap and straddling his waist. “I’ve never been attracted to another person before. I figured I... never would.” 

Gen hummed in understanding. “That’s why I was never really explicit with how I felt. You only ever had eyes for experimenting and inventing, I assumed any feelings you might have for me would just be platonic friendship at most.” 

Fair. That’s what he had thought originally too. “I guess we were both wrong.” Senku said, reaching up to tuck a strand of ivory hair behind Gen’s ear. 

With a smile, the mentalist leaned into his touch. “I’ve never been so happy to have misread someone.” 

It wasn’t fair, Gen was too beautiful, all but glowing in the moonlight, and Senku pulled his down into another kiss. The happiness he felt welling inside him was something totally foreign, somehow completely different from the happiness and excitement of bringing the twenty-first century back to life in the fifty-eighth century. Made sense, his body and had never been subject to the exact chemical concoction that kissing made his endocrine system release. 

He chuckled into the kiss. Later, he could do a full analysis on the effects Gen’s lips had on his body’s chemical feedback loops. Right now, well, his mind was finding it hard to do much else but focus on the feeling of Gen’s tongue in his mouth and soft hands on the nape of his neck. 

Without really noticing, Senku’s hands had drifted down Gen’s body, on hand coming to rest at the small of the mentalist’s back, the other sliding a bit lower. 

He could feel Gen smirk against his lips. “Is it okay if we do this here?” The mentalist asked. 

“What?” 

“I mean...” Gen pointed at the floor, referring to the other scientist that was only separated from them by a few planks of wood. 

“Chrome’s a heavy sleeper.” Which was true. Hopefully Chrome was currently asleep and would stay that way, because Senku had no intention of stopping. And it appeared that Gen felt the same way. 

“Good, good.” Gen murmured, and then, with a cheeky smile, “would you mind if maybe took off some of my clothes?” he rolled his shoulders back, making his overcoat slip down off his shoulders. “It’s getting sort of warm in here.” 

Senku’s heart skipped a beat. Or, it felt like it did, that didn’t actually happen. “I would one billion percent not mind. Not at all.” 

“Good.” 

Gen fumbled the rest of his way out of his overcoat, tossing it somewhere behind him. Senku set to helping the mentalist out of the rest of his clothes, starting with the length of rope tied in a bow around his waist. 

Double-knotted. Of course. He picked at the knot with blunt nails, eventually prying it loose. 

“Why do you have to wear so many layers?” Senku mumbled under his breath, tossing the rope to the side. 

“This body of mine is just too irresistible, I need to cover up or I would accidently seduce every single man and woman with my raw sexual power.” Gen joked in a slightly forced sultry voice, and though that wasn’t a satisfying or true answer, Senku let it slide. He got the feeling that he shouldn’t pry. At least, not now. 

Eventually he made his way through all of Gen’s redundant layers of clothing, and he was greeted by a smooth expanse of lily-white skin. Untouched by the stone world’s sun, Gen’s skin almost glowed in the light of the moon, and Senku found himself staring. Never would he have thought that he would be so enamored with someone's body in a non-scientific way. Well, you learn more about yourself every day. 

There was a small scar across Gen chest, all that remained of Magma’s attack on his life. Senku reached out to run his thumb along the raised skin. It was a good think that Gen was cautious and well prepared, or else the mentalist might have died way back then, on the first day they had met. A sudden pang of fear gripped Senku’s heart, a bit of dread at the thought of the hypothetical scenario in which the mentalist had never formally joined the Kingdom of Science. 

He was pulled out of his mind as Gen’s hands tugged at his belt, looking at him with a tiny pout. “It’s not fair if I’m the only one getting undressed.” 

Senku chuckled, and helped Gen in getting his tunic off. 

As he shrugged his clothing off of his shoulder’s, he could feel Gen’s eyes on him, tracing down his now bare chest. Had Gen ever seen him without clothing? Probably not, he made a point not to go walking around shirtless. For good reason, he got cold easily and he didn’t exactly have the kind of body one would show off. 

He wasn’t big or strong or muscular or built in any way that was attractive. He wasn’t even like Gen, who despite being thin and without any visible musculature still had an objectively appealing body. No, he was just skinny, with the bare minimum of muscles to function hidden beneath an absolutely average amount of fat and skin all clinging to a perfectly mediocre skeleton. 

He knew he was weak. He’d always known that. He’d just never been self-conscious about it until now. 

He’d never even thought about his body, except when he had to factor in his not so amazing physical strength as a variable in an experiment. Not until now, underneath Gen’s scrutinizing gaze. For the first time ever, he wished he had a better body for purely cosmetic reasons. 

“You’re beautiful.” 

That was a lie. Objectively, he wasn’t. He was average at best, really. Ask anyone, even Taiju and Yuzuriha, the kindest, most loyal people he knew, would struggle to say he had a good-looking body. And of course Gen would lie, that was the mentalist’s greatest skill. 

But, somehow, against all odds, the look on Gen’s face and the way he spoke those worlds, it seemed one billion percent sincere. 

“Trust me, Senku-chan. There are some things I won’t lie about.” he wrapped his arms around Senku’s neck, holding him close. “You are beautiful.” 

“You’ve got weird tastes, mentalist.” 

“Maybe I do. And what of it?” 

Senku chuckled, winding his arms around Gen’s thin torso, that bare skin warm under his hands. “Nothing. Just making an observation.” 

Bare chest to bare chest, he could feet Gen’s heartbeat, quick pulse mirroring his own. It was immensely comforting, sitting there in the observatory, under the stars, holding Gen close to him and having the mentalist nuzzle into the crook of his neck. He sighed happily, closing his eyes and relaxing against the mentalist’ body. Gen smelled good, like flowers and paper and grass and probably whatever the early morning smelled like. It was nice. Everything about this was nice. 

He felt as if he could sit there for the rest of eternity. 

But then Gen shifted in his lap, and he was reminded that he, and Gen, were both at least half-hard. Gen was still wearing his pants, and Senku could feel the mentalist’s clothed erection against his stomach. 

Sliding his hands down Gen’s back, he grabbed Gen’s ass and pressed their bodies closer. Gen whined in reply, rolling his hips forwards and wow, that felt amazing. Fuck. Senku bit his lip to stop a moan from escaping. 

“Senku.” Gen murmured against his neck. “I... I want...” 

Senku waited for him to finish his sentence, and when he didn’t, asked. “What do you want?” 

“I don’t know... what I can ask for.” 

“Anything.” he said, before he could stop the word from tumbling out of his mouth. He wasn’t going to stop indulging Gen now, of all times. 

“I...” Gen’s voice was hesitant, a little needy. “I want you to fuck me.” 

Sometimes, when his brain was too distracted by Gen to work, or when he was trying to fall asleep, or when he'd been painting the cards, he’d gone over some hypothetical situations in his mind. His hypothetical-mind-self telling Gen how he felt. Or sometimes, hypothetical-mind-Gen being the one to confess his feelings. And, rarely, hypothetical-mind-self getting rejected, because even though that wasn’t the preferred outcome it was good to be prepared for anything. But anyways. He’d imagined these scenarios, and the possible outcomes that may follow. And in doing so, he’d found himself wondering what sort of outcomes he wanted. 

He’d never thought about this sort of thing before. Being emotional, and subsequently physically, intimate with someone? Unheard of, until just recently. Now, though, he actually wanted it. But then that led to a slew of new questions. To what extent? How far did he want to go? What was he comfortable with? What would Gen be comfortable with? He had no empirical data to work with, for himself or for Gen or for the two of them together. He was going in completely blind, and it was all at once absolutely terrifying and exciting. 

“I want that too.” he replied, arms tightening around Gen. “I think I want that too.” 

“You think?” 

“This is all new, uncharted territory for me.” 

He could all but hear Gen smile. “That’s okay. Just let me know if you, you know, if you want to stop or anything.” 

“Okay.” 

Letting go of Gen, the mentalist stood up and kicked his pants off, now standing naked in the moonlight. As if he hadn't been beautiful enough already. 

Then, Gen crossed the observatory, grabbing the little jar of hand lotion from its spot in the corner. “Good thing you made this.” he grinned, shaking the little jar. “It’ll make things a lot easier for the both of us.” 

It took Senku a second to process what Gen was saying and insinuate what he meant. “Oh. Right.” 

“Do you want to, or should I?” 

Senku looked at jar blankly, once again figuring out what Gen meant after a second of processing. “Gen, I’ve never...” 

He knew, in theory, what to do. His research and the vast stores of knowledge in his brain covered a wide range of fields. And he was a teenage boy, after all, and had been a teenage boy back in the modern world with access to a computer. But theory and practice were two entirely different ballgames, and despite his confidence in all things scientifically-minded, he was not confident in a “soft” science like- 

Was he about to call sexual intercourse a soft science? 

It was at once both comforting and infuriating to hear Gen say “Don’t worry, I’ve had a bit of practice, I know what to do.” 

Of course he had, and of course he did. He had been famous, and wealthy, and he was objectively attractive. Yes, objectively, science always observed with an objective eye. Oh, and when Gen had first visited the Kingdom of Science, he had mentioned something about just wanting to hook up with cute girls or something of that ilk. Obviously, he had experience. 

Senku wasn’t jealous, of course. That was irrational. 

“Don’t be jealous.” Gen cooed, a cheeky grin on his lips. 

He didn’t want to lie, so he said nothing in return. He just let Gen pass him the jar and then sit in his lap, chest to chest, long, thin legs straddling his waist. 

He could infer what to do at this point. Uncapping the lotion, he dipped his fingers in, coating the first three as thoroughly as he could. 

Gen leaned against him, hugging him and resting his head against the scientist’s shoulder. “One finger at a time.” he instructed. “And be gentle. And use as much of the lotion as you can.” 

“Okay.” 

Setting the jar down, Senku held Gen with one hand as the other rested on his ass, between the cheeks. Sliding his middle finger down, he pressed against the entrance. 

He knew, in theory, the nature of the muscles of the anus, of the elasticity and the strength of the muscles. Applying as much pressure as he calculated would be necessary, his finger slipped in after a moment of resistance, and he felt Gen tense up in his arms. 

“Are you okay?” he asked, eyebrows knitting together. “Does it hurt?” 

Gen took a deep breath, relaxing. “No, it’s just been thousands of years since I did this last. Let me get used to it.” 

He did, patiently waiting for Gen to adjust and get comfortable. And then he followed Gen’s instructions, pressing in father, and waiting, and slipping a second finger in, and then after a bit, a third. If he was good at anything, it was following instructions step by step. 

And observing. He was good at observing and collecting data. Ans so he did, greedily committing to memory everything; every sound Gen made, every little shift of the mentalist’s body, the soft give of that pale skin in his grip, the feeling of Gen’s breath against his neck, how the arms around him tightened when he curled his fingers in the exact right way. He paid special attention to Gen’s breathing rhythm, and how he responded to every moment Senku made, and the time intervals between each subsequent finger. 

He had to learn what to do, and how to do it well, so that next time he would know what to do. 

He smiled, curling his fingers in a way that he had already observed to make Gen whine in pleasure. Was he being presumptuous, assuming there would be a next time? No, he was one billion percent sure that even if he somehow messed up miserably (which he assumed he wouldn’t) there would be a next time. 

“Okay, you’re good.” Gen mumbled, against his neck, voice soft, and Senku pulled his fingers out. After a brief moment of stillness, Gen pushed himself up and out of Senku’s lap, shakily standing up. The mentalist looked down, an amused smile on his face. “I have to say, I didn’t expect that the next time I’d have sex would be on the hard wood floor of a hut.” 

They used their clothes, and there was an old blanket in the corner of the observatory (from when it had been exceptionally cold). It was no modern-day mattress, but it was the best they could do at the moment. And Gen seemed content enough with the set-up, lying down on his back and arranging his rolled-up overcoat under his head in a makeshift pillow. 

“Well, I might feel it in the morning, but this should be good.” he smiled up at Senku, “And even if it wasn’t good enough, I wouldn't want to have to wait any longer.” 

Senku wasn’t sure he could wait any longer either. Well, of course he could. But he didn’t want to. 

Dipping his fingers back in the jar, Senku coated his cock with lotion and placed the jar on the ground beside him, within reach, just in case. Gen’s legs were spread around him, on knee on either side of his torso, and leaning forwards, he pressed the tip of his cock to Gen’s ass. All at once it hit him, it really hit him, just what was happening. As if his mind had been shocked into a buffering state and he hadn’t fully processed anything from when Gen had kissed him right up until this very moment. He’d confessed, in his own way. And Gen had reciprocated, in his own way as well. And now... and now... 

Gen’s hand came to rest on his knee, a small and reassuring gesture. Why Senku needed reassurance he didn’t quite know, but it was nice. It was comforting. It made him smile. 

One hand bracing on the floor, beside Gen’s hip, and one holding his own cock to guide it forwards, he thrust his hips. He felt, and watched, as the tip, after a brief moment of resistance, slid in. Gen tightened around him but then relaxed, and he pushed forwards, slowly, looking for any hint of pain that was worse than mild discomfort. He watched Gen’s hand, the one that wasn't resting on his knee, grip the blanket that was spread out beneath them. He watched Gen’s face, eyes squeezed closed, mouth drawn in a thin line, cheeks a deep pink. He bottomed out, and paused, letting out a breath he hadn’t realized he’d been holding. 

“Oh, Senku-chan, you’re so big.” Gen cooed, opening his eyes. Beneath long lashes, his eyes were slightly glassy, shining in the moonlight. 

“You’re just saying that.” 

“Maybe.” he smirked, tucking ivory hair behind his ear, “but there is a reason I made you take a long time to prep me so thoroughly.” 

Senku had no benchmark for how long it should take to prepare for anal sex, so he’d have to take Gen’s word for it. 

“You can move, you know.” 

“I can?” 

Gen smiled, and rolled his hips, making Senku let out a small, soft gasp. “Of course you can. What, were you just going to sit there all night?” 

Senku smiled back, leaning forwards, shifting his weight. “I was one billion percent not planning on doing that.” 

“Good.” 

It was unlike anything Senku had felt before. Of course, sex would be far different than masturbating solely due to the physical circumstances and the presence of another person, that much was evident. That much he had known, and expected. But he hadn’t expected this. No, in practice sex was far different from what theoretical knowledge had promised. 

Later, upon rethinking the whole thing, he would speculate that it was because he had only ever considered the physical and physiological aspects of sex, not the emotional and psychological aspects. 

It had been minutes, only a few minutes (263 seconds, approximately, he was having a bit of trouble keeping exact time), and already his body was feeling it. He could feel sweat dripping down his back in rivulets, feel his hair damp on the nape of his neck, feel his lungs burn as he took each deep, labored breath. It was a strange mix of muscles being overused and adrenaline forcing them to continue working at a maximum output. And mixed with the innate pleasure of sex, and the visual of Gen’s thin, pale body spread out before him, it was one of the most stimulating experiences of his life. 

Masturbating was just a means to an ends, an act of release that the body needed. Nothing more (for Senku, at least). Conversely, this was, well, this was far, far, _far_ more. He didn’t think he’d be able to stop his hips even if he wanted to. And why on earth would he want to? It felt amazing. 

Did sex always feel this good? Or was Gen just an excellent partner? He would have to have sex with other people to gather the empirical evidence needed to answer that hypothesis, and his mind, the small part that wasn't being overworked due to the present stimulus, decided that he really didn’t need to carry out such an experiment. 

Beneath him, Gen shifted, angling his hips off of the ground as he wrapped his legs around Senku’s waist. The change of angle seemed quite pleasant for Gen, as his breath caught in his throat and he tensed up just a little bit more. Taking in the cues, Senku readjusted their position just a bit more, hitching Gen up a little farther in his lap, and the mentalist threw back his head as he let out a loud moan which shocked Senku and hopefully had not woken up Chrome. 

“Good?” Senku asked, voice far shakier than he had expected. 

Gen let out a breathless laugh, “Good.” he replied. “Oh, Senku, it’s so good.” 

With each subsequent thrust, Gen repeated his name like a mantra, voice breathy and soft and reverent. Senku focused what little brain activity he could spare on those words, on the sound, on the way Gen’s tongue formed his name, on the way his name tumbled from those lips. He loved Gen’s voice, and call him conceited, but the way the mentalist said his name was the most beautiful of any of the words he spoke. 

And he didn’t miss the way Gen’s breath hitched, the way his voice climbed in pitch and tone, when he wrapped his long, thin fingers around his cock. 

Senku watched, without stopping the motion of his hips, as Gen stoked himself. The mentalist was a sight to behold, entire body flushed a pale pink, barely visible muscles taut and shaking as he worked himself closer and closer to release. He wasn’t breathing Senku’s name anymore, just focusing on breathing, as his hand moved faster and faster up and down his shaft. He was close, Senku could tell that much. 

And, back arching, head thrown back, Gen came, legs tightening around Senku's waist so much it was hard to continue to move. But a moment later the mentalist relaxed, completely, body going limp as he let out a long, breathy moan. So limp Senku was sort of worried. He should do something, right? Like stop? 

“Don’t stop.” the mentalist breathed, giving Senku a weak, sated smile. “Don’t you dare.” 

So he didn’t. He held Gen’s hips, half his mind telling him to hold as tightly as he could and the other half reminding him to make sure not to hurt Gen or bruise him. He wasn’t sure what he ended up doing, his thoughts were far too addled at this point to really make sense of anything other than the pleasure building in the pit of his stomach and one of Gen’s hands resting gently on his left knee. 

The pleasure built and built until it spilled over, and the back of his eyelids flashed white, and at the last second some part of his brain suggested that he shouldn’t come inside, something about how condoms existed for a reason. So he pulled out, and with a grunt he came all across Gen’s stomach, having to brace himself with a hand on the floor to stop from immediately collapsing on top of the mentalist. 

After a moment of stillness, the observatory filled with the sound of their labored breathing, Senku sat back on his heels, wiping his forehead with the back of his hand. As he struggled to regulate his breathing, his mind finally slowed down enough to be fully cognizant of his surroundings. Of his aching muscles, not used to so much physical activity. Of his knees, which had not been saved from the hard wooden floor by the makeshift mattress. Of his hair, which was far less voluminous than usual and was falling in front of his face, deflated from said physical activity. Of Gen, laying before him, looking as tired and content as Senku himself felt, a small smile on his lips as he looked up at Senku. 

Shakily, he laid down next to Gen, his chest still heaving from the exertion. 

Gen chuckled. “You look so different with your hair down.” 

Senku halfheartedly ran a hand through his sweaty, messy hair, trying to get it to stand back up. But he was fighting a losing battle. 

“I kinda like it.” Gen said. 

“It looks dumb.” 

“Maybe. Maybe that’s why I like it.” 

They lay in silence for a while. Senku felt Gen shift beside him, into a seated position, and clean up a bit, wiping his stomach off with one of the pieces of fabric that had made up their makeshift bed (a piece of fabric that was part of Senku’s clothes. But Senku didn’t say anything. It wasn’t as if Gen would use his own clothes, after all. Of course not. It was fine). 

Satisfied, Gen lay back down, on his side, and scooted right up next to Senku. Close enough that he could drape a long, pale leg across Senku’s hips. 

Reaching out, Senku tucked a lock of black hair behind Gen’s ear. Then, gently running his thumb over the mentalist’s cheek, he traced the jagged path the petrification scar cut across his skin. Down Gen’s cheek, over the ridge of his jaw, and down his neck, feeling the soft skin yield to his touch. The edges of the scar were only slightly rougher than the rest of the skin, and the tiny divot was, despite how severe it looked, almost imperceptible to the touch. 

“I had a plan for telling you how I felt.” Senku said, softly, “And you ruined it.” 

Gen raised an eyebrow, intrigued. “A plan that involved more than giving me a beautiful deck of cards?” 

“Yes. But then you kissed me, and the rest of the plan became moot.” 

“Oh, now I’m sad. I would have loved to see what Senku-chan had planned out for his confession.” 

“And now you never will.” 

Gen looked shocked. “You won’t tell me?” 

“No. It’s extraneous.” And, in hindsight, a tad embarrassing. 

“That’s not fair!” 

“How? How could it possibly be unfair?” 

“I want to know!” 

A muffled voice from beneath the observatory called out, “Can you two shut up?! I’m trying to sleep down here!” 

They both froze, looking mortified. Gen managed to call back, in a semi-normal voice. “Sorry, Chrome-chan. The stars were just so pretty, we got a little excited and-” 

“Yeah, yeah, whatever you say. Just shut up.” 

Gen smiled sheepishly. “Do you think he heard... everything?” he asked, whispering so softly Senku could barely hear him. 

“I hope not.” He didn’t want anyone else to hear Gen calling out his name. Call him selfish, but he wanted to be the only one to witness that. 

“Well, if he did, I’ll make sure he never says anything about it.” His smile turned dark and devious. 

Whether Chrome had or hadn't bore witness to the entirety of the proceeding events was a matter for tomorrow. It was late by now, about two in the morning based on the position of the moon. And Senku yawned, the adrenaline from sex having run its course, leaving him exhausted. 

“Bed time?” Gan asked, falling prey to the contagious nature of yawns. 

“Bed time.” He moved to stand up. “I’ll close the roof-” 

“Leave it open.” Gen said, pulling him back down. “The stars are so pretty. And it’s romantic, falling asleep under the stars.” 

Senku snorted. How sappy. But he let Gen pull him down into their makeshift bed, and he couldn’t argue that laying there, together, lit by the starlight up above, did feel akin to whatever "romantic” was supposed to mean. 

Rolling onto his side, Gen curled up beside Senku, sighing happily. “Thank you.” 

“Hmm?” 

“For the cards. I never actually thank you for them.” 

“Oh. You’re welcome.” 

Gen shifted, and ended up resting his head on Senku’s chest. “They’re the second-best thing I could have gotten as a gift.” 

“Second best? What would have been the best?” 

He could feel Gen smile against his skin. “You.” 

He laughed at the corniness of it, and Gen followed suit. “Gross.” 

“Isn’t it though?” Gen chuckled. 

In reply Senku just kissed the top of the mentalist’s head. “Go to sleep.” Now that he was lying down, he could feel himself drifting off. He had a feeling he would have a great sleep, until the sun rose high enough to shine in their faces. 

He was already almost asleep when he heard Gen whisper, in a half-asleep-sounding voice, “I love you.” 

Senku’s lips curled up in a smile, and he replied, as best he could in his current state. “I love you too.” So maybe it had taken him far too long to realize his feelings. And then act on them. But hey, it was better late than never. It was far, far better than never. 

**Author's Note:**

> Did we ever find out how Gen got his deck of cards? I dunno but I'm just assuming that Senku made them for him because they’re gay. 
> 
> I've got a bit of Sengen art up over at https://darknebulablader.tumblr.com if you want that in your life.


End file.
